Since a long time ago, glass fiber-containing resin compositions have been known in the art, in which polyolefin resins are improved in their mechanical strength. In these years, organic fiber-containing polyolefin resin compositions have attracted attention from a viewpoint of a problem of industrial waste products. Particularly, from a viewpoint of a problem of global warming due to carbon dioxide, there have also been investigated polyolefin resin compositions reinforced by carbon-neutral and plant-originated organic fibers. However, organic fibers are easily entangled, and are very difficult to be detangled. Therefore, investigations have been made to blend organic fibers homogeneously with polyolefin resins.
For example, JP8-11131A discloses a composition containing two or more kinds of organic fibers blended homogeneously with a thermoplastic resin powder, which composition is a starting material for producing a fiber-reinforced thermoplastic resin. JP2006-96836A discloses organic fiber-containing pellets produced according to a method of (i) drawing organic fibers to align them, (ii) solidifying them with a binder resin, and then (iii) pelletizing them, which pellets are not so bulky as organic fibers, and therefore can easily be used to make composite compounds. JP2007-84713A discloses a process for producing a cellulose fiber-containing thermoplastic resin composition, comprising the steps of (i) putting aggregative cellulose fibers in a rotary impeller-carrying mixer, (ii) rotating the mixer at a high speed, thereby detangling the cellulose fibers, (iii) putting a thermoplastic resin in the mixer, (iv) agitating the thermoplastic resin to melt it by friction heat, the molten resin adhering to the detangled fibers, thereby forming a mixture containing the fibers and the resin, and (v) agitating the mixture at a low speed under cooling it.